This invention relates to the preparation of polyether polymers and more particularly to an improved method for such preparation in a phase transfer catalyzed reaction. In a particular embodiment the invention relates to the preparation of polyetherimides in a phase transfer catalyzed reaction.
Polyetherimides have become an important genus of engineering resins because of their excellent properties. Conventionally, they have been prepared by the reaction of an aromatic diamine with an aromatic dianhydride. This method, however, has a disadvantage in that it requires many steps for preparation of the dianhydride, including, for example, the conversion of phthalic anhydride to an N-alkylimide, nitration of said N-alkylimide, displacement of the nitro group with an alkali metal salt of a dihydroxy-substituted aromatic hydrocarbon and an exchange reaction with phthalic anhydride to afford the dianhydride.
It has also long been known to prepare polyetherimides by a displacement reaction of an alkali metal salt of a dihydroxy-substituted aromatic hydrocarbon with an aromatic bis(substituted phthalimide). As originally developed, this reaction required the use of expensive dipolar aprotic solvents and the product tended to develop color and be contaminated with various by-products.
U.S. Pat. No. 5,229,482 discloses a displacement method for the preparation of polyetherimides from bis(chlorophthalimides) using a solvent of low polarity such as o-dichlorobenzene, in the presence of a thermally stable phase transfer catalyst such as a hexaalkylguanidinium halide. U.S. Pat. No. 5,830,974 discloses a similar method using a monoalkoxybenzene such as anisole as solvent. These methods made it possible, for the first time, to envision the commercial production of polyetherimides by the displacement method.
Nevertheless, several problems remain to be solved for the optimum development of the displacement reaction for polyetherimide preparation. First, there has been no method for control of molecular weight of the product, other than limiting reaction time. Second, the amount of phase transfer catalyst required for polyetherimide preparation in substantial yield is high, typically on the order of 5 mole percent based on bis(chlorophthalimide). Third, the product typically contains relatively large proportions, typically 8-10% by weight, of cyclic oligomers. While the preparation and ring-opening polymerization of cyclic polyetherimide oligomers may be a useful alternative to other polymerization methods, the presence of such oligomers as by-products in the linear polymer can adversely affect its properties and increase its polydispersity (Mw/Mn). Fourth, endcapping methods that might minimize problems resulting from the presence of reactive end groups have not been known. Fifth, the effects of such variables as impurity level and stoichiometric imbalance of the reagents have been unknown.
It is of interest, therefore, to continue development of the displacement method of polyetherimide preparation and optimize the same.